Many things have combined to make very high-frequency RF gear much more common, cheaper, and better performing. Case in point: [dereksgc] is tearing apart a 20 GHz low-noise block (LNB). An LNB is a downconverter, and this one is used for some Irish satellite TV services.
The scale of everything matters when your wavelength is only 15 mm. The PCB is small and neatly laid out. There are two waveguides printed on the board, each feeding essentially identical parts of the PCB. Printed filters use little patterns on the board that have particular inductance and capacitance — no need for any components. Try doing that at 2 MHz!
The LNB is a single-band unit, so it only needs to worry about the two polarizations. However, [dereksgc] shows that some have multiple bands, which makes everything more complex. He also mentions that this LNB doesn’t use a PLL, and he’d like to find a replacement at this frequency that is a bit more modern.
After the teardown, it is time to test the device to see how it works. If you want to experiment at this frequency, you need special techniques. For example, we’ve seen people try to push solderless breadboards this high (spoiler: it isn’t easy). Maybe that’s why many people settle for modifying existing LNBs like this one.
Learn the term “mixer”
It is a little unclear to me what you mean.
The LNB is more than a mixer. There is handling of signal polarization, RF amplification, filters, a high side local oscillator, a mixer, and supporting circuitry. Even calling it a down converter understates its function.
Why all the holes in the conductors?
The “holes” are vias. They connect a trace on one side to a trace on the other side.
The traces with vias are on this board (mostly) ground traces. The vias connect the ground traces with the ground plane on the bottom side.
Tying the traces to the ground plane helps to maintain a constant impedance between the ground traces and the signal traces.
Thanks. It would have helped if the video had shown the underside of the board. I’d like to see just how much coverage the ground plane has.
It’s been a while (6 years) since I worked with satellite equipment.
This reminded me of:
Triax (RIP) made a LNB PCB with wide band tuner FPGA, and POE Ethernet.
They joked “Why is the PCB so expensive when it’s mostly made of holes?”
Am scared, what does one need to really understand what most of the words are?
“[dereksgc]… also mentions that this LNB doesn’t use a PLL, and he’d like to find a replacement at this frequency that is a bit more modern.”
This is NOT about “modern”, instead it’s usually all about “money” (or lack thereof). A two-way VSAT ground terminal will often use a PLL synthesized local oscillator that is “disciplined” by a local 10 MHz high stability/low phase-noise ~0dBm reference signal which is often multiplexed on the L-band IF cable (or cables). This is usually the case when the VSAT ground terminal uses more sophisticated (hence costly) TDM or TDMA technology (or similar). Lower cost VSAT ground terminals that do not need a higher cost high-stability/low phase-noise phase-locked (PLL) reference oscillator(s) will typically use cheap dielectric resonator local oscillators (DROs) in their LNBs and/or SSPA blocks. If you are provisioning or servicing any sort of two-way VSAT terminals ALWAYS follow what the OEM says about using DRO versus PLL outdoor equipment (LNBs and SSPAs). Yeah, a cheap DRO LNB may work for a while, but typically it WILL eventually fail as it drifts off frequency.
Marvelous, amazing, when i see an electronic video on youtube, next days later hackaday speak about….